This invention relates to methods and apparatus for use in conjunction with display devices. Most particularly, these inventions relate to methods and apparatus for uniformly aging one or more cathode ray tubes (CRT""s) within a display device, such as a television.
This application is related to Application Ser. No. 09/450,942, which is expressly incorporated herein by reference and filed on the same date.
All televisions utilize one or more cathode ray tubes (CRT""s) to transform video information into light rays for display on the television screen. This is typically accomplished by exciting the phosphor material on the CRT with a scanned beam of electrons, causing the phosphor material to output light. Typically, over time, usage of the CRT causes aging or reduction of light output from the CRT phosphor material. When the entire nominal scan area of the CRT phosphor is excited (i.e., the area of the CRT phosphor corresponding to the geometry of the television screen), the CRT phosphor material is uniformly aged, resulting in an unnoticeable uniform reduction of light from the CRT. Under these circumstances, this phenomenon is typically not problematic. When only a portion of the nominal scan area of the CRT phosphor is excited over a period of time, however, the CRT phosphor is non-uniformly aged, resulting in a noticeable non-uniform reduction of light from the CRT.
This problem typically arises when video signals formatted with one aspect ratio are displayed on a television formatted in another different aspect ratio. The aspect ratio of a television picture image is a ratio of horizontal length to vertical length, expressed in relative units. Standard video signals, such as NTSC and PAL video signals, are formatted with a 4:3 aspect ratio (i.e., 1.33 aspect ratio), whereas non-standard video signals, such as HDTV video signals, are formatted with an aspect ratio greater than the standard 4:3 aspect ratio. For example, an HDTV video signal is typically formatted with a 16:9 aspect ratio (i.e., 1.77 aspect ratio). Modern cinematographic theater movies, not made expressly for conventional television, are typically films with aspect ratios greater than 1.33, typically ranging between 1.65 and 2.35.
When standard video signals are displayed on a standard television screen (i.e., a television screen having a 1.33 aspect ratio), the picture image appears on the entire television screen. As long as these standard video signals are displayed on a standard television screen, the associated CRT or CRT""s are uniformly illuminated, and thus uniformly aged. When a non-standard video signal, such as an HDTV video signal, is displayed on a standard television screen, the picture image appears on the middle horizontal region of the television screen and black bars appear on the respective top and bottom horizontal regions of the television screen. As a result, a region of the CRT that would normally be illuminated in response to a standard video signal is not illuminated in response to the non-standard video signal.
Thus, without correction, display of a non-standard video signal on a standard television screen over an extended period of time causes the phosphor material disposed on a primary region of the CRT (represented by a middle horizontal region of the nominal CRT scan area) to age more than the phosphor material disposed on a secondary region of the CRT (represented by respective top and bottom horizontal regions of the nominal CRT scan area). When a standard video signal is then displayed on a standard television screen on which non-standard video signals have been displayed over an extended period of time, the top and bottom horizontal regions of the television screen will be distinctly brighter than the middle horizontal region of the television screen. These distinctions will appear as two respective spatial transition lines between the top and middle horizontal regions of the television screen and between the bottom and middle horizontal regions of the television screen. Most viewers will complain about this phenomenon, which may require a service call to replace the CRT or CRT""s. If the television is a projection television (PTV), which typically includes three color CRT""s, this service call may cost $500 or more.
One method used to reduce this non-uniform CRT phosphor aging problem involves slowly moving the electron scanning angle over time, so that the spatial transition lines are blurred. Another method involves pre-aging the CRT phosphor with white video, which takes advantage of the fact that the problem of non-uniform CRT illumination lessens with time. These methods, however, only reduce the problem of non-uniform CRT illumination, and do not necessarily eliminate the problem. Still another method involves illuminating the respective top and bottom portions of the CRT with gray video when an HDTV video signal is displayed. This method, however, reduces the amount of resolution that is available for display of the actual HDTV video signal. For example, if the entire area of the CRT is provided with a resolution of 1080 interlaced lines, only 810 interlaced lines will be provided for display of the HDTV video signal.
Accordingly, an improved method and apparatus for uniformly aging the phosphor material on a CRT is desired.
Methods and apparatus are utilized for uniformly aging the phosphor material on a CRT. The CRT may be located in a display device, such as a television, a computer monitor, or any other device that uses a CRT to transform a video signal into light output. The method serves to uniformly age a CRT that has been previously illuminated at a mismatched illumination ratio. This mismatched illumination ratio occurs when the CRT is illuminated in response to a video signal formatted in an aspect ratio different from the aspect ratio of the display screen. By way of non-limiting example, if the display screen has an aspect ratio of 4:3, illumination of the CRT in response to a video signal formatted in a 16:9 aspect ratio, such as an HDTV video signal, will cause a mismatched illumination. In this scenario, a primary region of the CRT corresponding to the middle horizontal region of the television screen is illuminated, and a secondary region of the CRT corresponding to the respective top and bottom horizontal regions of the television screen is non-illuminated.
To facilitate the uniform aging of the CRT, one or more CRT aging indicators, which indicates the extent to which the CRT has been illuminated at the mismatched illumination aspect ratio are obtained. These one or more CRT aging indicators may include, for example, an unequalized CRT burn time, i.e., an amount of time the CRT was illuminated at the mismatched illumination aspect ratio, or a combination of an unequalized CRT burn time and an average CRT luminous intensity level exhibited by the CRT when illuminated at the mismatched illumination aspect ratio. The one or more CRT aging indicators may include a pair of luminous intensity levels measured at the respective primary and secondary CRT regions in response to an internal video signal, preferably a uniform white video signal.
The secondary CRT region is illuminated based upon the one or more CRT aging indicators. In the preferred method, this is accomplished by generating an internal video signal, during a television off-state, which effects illumination of the secondary CRT region at a greater intensity than that of the primary CRT region. This can be accomplished by illuminating the secondary CRT region without illuminating the primary CRT region. In the preferred method, a desired CRT age equalizing time, i.e., the amount of time the secondary CRT region should be illuminated to equalize the CRT aging, is calculated based on the one or more CRT aging indicators. Precalculation of the desired CRT age equalizing time can be accomplished by aging like CRT""s, given known sets of CRT aging indicators, and storing the desired CRT aging equalizing time and corresponding sets of CRT aging indicators within a look-up table. Thus, the secondary CRT region can be illuminated an amount of time equal to the desired CRT age equalizing time to effect equalization of the CRT aging.
Because, in the preferred method, the secondary CRT region is only illuminated during a television off-state, this aging process may be interrupted when the television is placed in the on-state. Thus, in the preferred method, a net cumulated CRT age equalization time is stored, wherein the calculated desired CRT age equalization time can be added thereto and an actual CRT age equalization time can be subtracted therefrom. Thus, the net cumulative CRT age equalization time represents the amount of time the CRT secondary region should be illuminated to equalize the CRT aging at the time the television is placed in the off-state from the on-state, or in the on-state from the off-state. When the net cumulative CRT age equalization time is utilized, the secondary region of the CRT will be illuminated at a luminous intensity level (preferably at a higher intensity level than that at which the CRT is illuminated during normal operation, to minimize the time necessary to uniformly age the CRT) for a period of time equal to the lesser of the net cumulative CRT age equalization time and the television turn-off time. In the preferred method, various means, such as, CRT covers, exterior doors, and interior doors, can be employed to prevent the internally generated video signal from being displayed on the television screen.
In an apparatus, a CRT, video signal terminal, video pattern generator and control circuitry, such as a microcomputer, are provided. In the preferred embodiment, the television screen has a standard 4:3 aspect ratio. The video signal input receives an external video signal and is coupled to the CRT for illuminating the CRT in response to the external video signal. The external video signal is such that the secondary CRT region is not illuminated, such as if the external video signal is non-standard and the CRT is standard. Of course, if the television screen has a non-standard aspect ratio, such as 16:9, a secondary CRT region may not be illuminated if the external video signal is standard. The video pattern generator generates the internal video signal and is coupled to the CRT for illuminating the secondary CRT region. The control circuitry is configured for calculating the desired CRT age equalization time and is coupled to the video pattern generator for generation of the internal video signal for an amount of time equal to the CRT age equalization time. In the preferred embodiment, the control circuitry directs the video pattern generator to generate the internal video signal when the television is in the off-state and directs the video pattern generator to cease generating the internal video signal when the television is in the on-state.
A first timer can be coupled to the control circuitry, such that it can be activated when the external video signal is received and deactivated when the external video signal is not received. In this manner, the unequalized CRT burn time can be tracked. A sensor can also be coupled to the control circuitry for tracking the average CRT luminous intensity level. The control circuitry can utilize these CRT aging indicators to calculate the desired CRT age equalization time.
To prevent viewing of the internal video signal, which may otherwise be annoying to the viewer, display of the internal video signal is blocked by use of means, such as CRT covers, external screen doors or internal screen doors. These blocking means may be automatically controlled upon generation of the internal video signal, or may be manually or remotely performed by the user upon detection of internal video signal display on the television screen. Preferably, the blocking means blocks the entire CRT or television screen to prevent any leakage of light, which may otherwise be visible to the user.